Bearing arrangement for reaction mass in a controlled environment

ABSTRACT

A reaction mass apparatus for stabilizing a scanning system during lithographic processing comprises a baseframe; at least one reaction mass movably coupled to the baseframe by at least three first bearings and coupled to a stage by at least two second bearings and at least one drive; and a plurality of bellows, each bellows surrounding a corresponding first bearing, the bellows each having a first end coupled to a reaction mass and a second end coupled to the baseframe. The apparatus can comprise an enclosure, containing a controlled environment and enclosing the stage, the second bearings, the drive, and the reaction mass, wherein each bellows separates a corresponding first bearing from the controlled environment and wherein each bellows second end is coupled to the enclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to lithographic processing. Moreparticularly, this invention relates to an improved bearing arrangementfor a reaction mass used for lithographic processing within a controlledenvironment.

2. Background Art

Lithography is a process used to create features on the surface ofsubstrates. Such substrates can include those used in the manufacture offlat panel displays, circuit boards, various integrated circuits, andthe like. A frequently used substrate for such applications is asemiconductor wafer. During lithography, a wafer is disposed on a waferstage and held in place by a chuck. The chuck is typically a vacuum orelectrostatic chuck capable of securely holding the wafer in place. Thewafer is exposed to an image projected onto its surface by exposureoptics located within a lithography apparatus. While exposure optics areused in the case of photolithography, a different type of exposureapparatus can be used depending on the particular application. Forexample, x-ray, ion, electron, or photon lithographies each may requirea different exposure apparatus, as is known to those skilled in therelevant art. The particular example of photolithography is discussedhere for illustrative purposes only.

The projected image produces changes in the characteristics of a layer,for example photoresist, deposited on the surface of the wafer. Thesechanges correspond to the features projected onto the wafer duringexposure. Subsequent to exposure, the layer can be etched to produce apatterned layer. The pattern corresponds to those features projectedonto the wafer during exposure. This patterned layer is then used toremove exposed portions of underlying structural layers within thewafer, such as conductive, semiconductive, or insulative layers. Thisprocess is then repeated, together with other steps, until the desiredfeatures have been formed on the surface, or in various layers, of thewafer.

Step-and-scan technology works in conjunction with a projection opticssystem that has a narrow imaging slot. Rather than expose the entirewafer at one time, individual fields are scanned onto the wafer one at atime. This is done by moving the wafer and reticle simultaneously suchthat the imaging slot is moved across the field during the scan. Thewafer stage must then be stepped between field exposures to allowmultiple copies of a reticle pattern to be exposed over the wafersurface. In this manner, the sharpness of the image projected onto thewafer is maximized.

While using a step-and-scan technique generally assists in improvingoverall image sharpness, image distortions may occur in such systems dueto movement of the entire system caused by the acceleration of thereticle stage or wafer stage. One way to correct this is by providing acounter balance (also referred herein as a reaction mass) to minimizethe movement of the lithographic system upon acceleration of a stage.The reaction mass reacts to the force applied by the acceleration of astage to prevent that force from affecting the overall lithographysystem during processing. In this way, reaction mass mechanismseliminate stage-induced system vibration, which has the beneficialeffect of increasing focus budgets and image contrast. Using a reactionmass mechanism allows rapid-motion scanning without transferringreaction forces to the machine baseframe, thus avoiding shaking thelithography system with every pass of the stage, which would disturbsensitive processing.

Typically, reaction mass mechanisms are guided by bearings or flexures.Flexures are thin vertical plates, attached at a protrusion at each endof a reaction mass such that when a stage coupled to the reaction massaccelerates, the reaction mass moves in the opposite direction as thestage, in a manner supported and guided by the flexures. The movement ofthe reaction mass in the opposite direction helps to stabilize thelithography system during processing. The ends of the flexures that arenot coupled to the reaction mass are coupled to another entity, such asa baseframe. In this way, both ends of a flexure are constrained so thatthe flexure cannot rotate upon movement of the reaction mass. Flexuresusually include one or more groove-like channels at each end forflexiblity in supporting the reaction mass. The channels can be angular,rounded, or of any shape that will allow flexibility in the flexure.

An advantage of using flexures is that flexures can be used to guide oneor more reaction masses in controlled environments such as purged gasmini-environments or high vacuum chambers. An advantage that the use offlexures has over the use of bearings is that flexures will notcontaminate the environment as would, for example, the gas of a gas (orair) bearing or the lubricant of a roller bearing. Typically, flexuresthat are used in these controlled environments are flexures that arecapable of accommodating a limited range of motion. By increasing themass of the reaction mass, the required range of motion of the reactionmass is reduced to the point that flexures can be used. A reaction forceis the product of the mass of the stage and the acceleration of thestage. Since the reaction force is also equal to the product of the massof the reaction mass and the acceleration of the reaction mass,increasing the mass of the reaction mass reduces its acceleration,velocity and displacement.

However, the use of flexures presents a variety of problems in additionto extra-heavy reaction masses. For example, upon acceleration of astage coupled to a reaction mass, the reaction mass will move in anarcuate path instead of the desired straight line due to the flexibilityof the flexures. In other words, the flexures each shorten with aquadratic error. The effect of the quadratic error is an unbalancedup-and-down motion of the reaction mass. The arcuate motion caused bythe quadratic error results in undesirable vertical reaction forces. Thestraying from straight line motion causes transverse forces to transferto the baseframe of the system. Not only could this cause unwantedmovements of the system during lithographic processing, but this alsomay cause a clearance problem between the bouncing reaction mass and alinear motor, if used to drive the stage. Complex flexure systems havebeen proposed, which in theory produce a straight line. However, inpractice, the straight line motion is highly sensitive to manufacturingtolerances. For example, all flexures used would have to be exactly thesame length, bend in exactly the same way, and be attached perfectly fora purely straight line motion to result.

Another shortcoming of flexure use is that the bending of flexures,alone, transfers some of the reaction force to the baseframe. Anothershortcoming when using a heavy reaction mass is that it is difficult toachieve infinite fatigue life of the flexures. To achieve an infinitefatigue life, the flexures would have to be very long, which becomesdifficult to package.

The use of bearings, on the other hand, provides a simpler arrangementthat naturally produces substantially straight motion. One shortcomingof bearing use in general, however, is that a number of bearings areneeded to guide the reaction mass (e.g., some are needed underneath thereaction mass, some are needed on the sides, etc.). With a splitreaction mass stage, where at least two reaction masses are used, atleast twice as many bearings are needed.

Although various types of bearings can be used (e.g., ball bearings,roller bearings, wheels, etc.), gas bearings are preferred inlithography systems because of good rectilinear motion. When using gasbearings, movement remains planar as long as the surface traveled overis fairly planar. Gas bearings do not present “lack of roundness” and“stick-slip” issues as one may have with wheel or ball bearings. Theextremely low friction of gas bearings also conserves momentum,minimizing motor size. In addition, transmitted vibration issignificantly reduced when using gas bearings because air is usedinstead of a solid object such as a ball. Potential contaminants, suchas the lubricant in a ball or roller bearing are not present with gasbearings.

Although cylindrical gas bearings have been used with cylindrical rodsas guideways inside high vacuum systems, their use is not favored forsupporting the reaction masses of lithography systems. The main problemis that the cylindrical configuration is not well suited for supportinga heavy reaction mass. Large guide rod diameters are required forsufficient lift and to minimize guide rod deflection under the heavyload. Dynamically sealing against gas leakage into the vacuum chamberrequires at least two pre-vacuum grooves in each cylindrical airbearing, which in turn demand additional vacuum pumps, resulting in anexpensive system. The dynamic nature of the seal can result in someleakage of air bearing gas into the vacuum chamber, which increases therequired size of the main vacuum pumps. Potential failure of the sealposes a high risk of catastrophic contamination within the controlledenvironment.

What is needed is a reaction mass system used in conjunction with linearstages that stabilizes a lithographic system during processing in acontrolled environment, without the deficiencies associated withreaction mass systems described above.

BRIEF SUMMARY OF THE INVENTION

A system for stabilizing a scanning system during lithographicprocessing is described. The system according to the present inventionincludes a baseframe, at least one reaction mass, and a plurality ofbellows. The reaction mass is movably coupled to the baseframe by atleast three first bearings and coupled to a stage by at least two secondbearings and at least one drive. Each bellows surrounds a correspondingfirst bearing. In one embodiment of the present invention, each bellowshas a first end coupled to the reaction mass and a second end coupled tothe baseframe. In one embodiment of the present invention, the firstbearings are fluid bearings in which, according to one embodiment, thefluid is a pressurized gas, and according to another embodiment, thefluid is a liquid film. For high lifting efficiency and low cost, allfluid bearings and guideways on which they ride are planar instead ofcylindrical. In another embodiment, the first bearings are rollerbearings. In yet another embodiment, the first bearings are ballbearings. In still another embodiment, at least one first bearing ispositioned such that it linearly guides a reaction mass.

The system according to the present invention can further include anenclosure having a controlled environment. The enclosure encloses thestage, the second bearings, the drive, and the reaction mass. In thisembodiment, each bellows separates a corresponding first bearing fromthe controlled environment and each bellows' second end is coupled tothe enclosure. In an embodiment, the volume of each bellows has apressure that is independent of the pressure of the volume of theenclosure. This means that the volume of each bellows can be atatmospheric pressure even if the controlled environment is not atatmospheric pressure. In one embodiment, the baseframe is uncoupled fromthe enclosure. In another embodiment, the baseframe is coupled to theenclosure via rigid supports.

In yet another embodiment, the baseframe is coupled to the enclosure viaflexible supports. The enclosure can further enclose lithographicexposure means, including an illuminator with which to illuminate a masklocated on a mask stage and a projection optics with which to project animage of the illuminated mask onto a substrate located on a substratestage.

In a system according to the present invention, the drive comprises alinear motor coil coupled to the stage and a magnet coupled to areaction mass, wherein the linear motor coil and the magnet are coupledmagnetically.

In a system according to the present invention, the mass of the stage isX times less than the mass of the reaction mass, resulting in thereaction mass moving, upon acceleration of the stage, a distance 1/X thedistance of the stage.

Each bellows is sized such that it can move with the reaction mass uponmovement of the stage.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES.

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1A is an exemplary illustration of a linear spring with flexuresthat follow a frown-shaped arcuate path upon movement of a stage.

FIG. 1B is an exemplary illustration of a linear spring with flexuresthat follow a smile-shaped arcuate path upon movement of a stage.

FIG. 2 is an exemplary top-view illustration of a split reaction masssystem showing the direction of movement of the reaction masses uponmovement of a stage.

FIG. 3 is an illustration of a reaction mass assembly with bellows in acontrolled environment according to an embodiment of the presentinvention.

FIG. 4 is a close-up illustration of bellows and bellows connections.

FIG. 5 is a partial illustration of a side view of a reaction massassembly with bellows according to an embodiment of the presentinvention.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those skilled inthe art with access to the teachings provided herein will recognizeadditional modifications, applications, and embodiments within the scopethereof and additional fields in which the present invention would be ofsignificant utility.

Newton's Third Law of motion states that for every action, or force, innature, there is an equal and opposite reaction. In other words, ifobject X exerts a force on object Y, then object Y also exerts an equaland opposite force on object X. Reaction mass systems used in mechanicalor electromechanical systems, including lithographic processing systems,work under the same principle.

Conventional reaction masses 110, 210 are illustrated in FIGS. 1A, 1B,and 2. Flexures can be used to guide one or more reaction masses 110,210 in high vacuum environments. As depicted in linear spring 100A ofFIG. 1A, each reaction mass 110A in a system can be supported by twolarge vertical flexure plates 115A attached at either end of thereaction mass 110A. One end of each flexure 115A is also coupled to abaseframe 105A of the system. In this way, both ends of a flexure areconstrained so that the flexure cannot rotate upon movement of thereaction mass. A stage (not shown) is also coupled to the reaction mass110A such that when the stage accelerates during processing, thismovement causes the reaction mass 110A to accelerate in the oppositedirection, in an attempt to stabilize the system. This movement isdepicted in top-view split reaction mass system 200 of FIG. 2. In asplit reaction mass system, typically there are two reaction massesplaced in parallel, with a stage located between them. Note that areaction mass can be of any shape and does not have to be shaped asdepicted in the accompanying figures.

In FIG. 2, stage 220 is coupled to reaction masses 210 via bearings 225.

In this example, stage 220 is driven via a conventional linear drivemotor consisting of linear coils 230 and magnet arrays 235, each magnetarray attached to a reaction mass 210. When stage 220 accelerates indirection 240, the reaction masses accelerate in the opposite direction245 to compensate, eliminating external reaction loads, and therebystabilizing the system.

The use of flexures presents a variety of problems. Referring again toFIG. 1A, when both flexures 115A are attached to the baseframe 110A attheir bottom end and to the reaction mass at their top end, reactionmass 110A follows a frown-shaped arc 116A upon acceleration of a coupledstage (not shown). In other words, the flexures 115A each shorten with aquadratic error. The effect of the quadratic error is an unbalancedup-and-down motion of the reaction mass.

Not only could this cause unwanted movements of the system duringlithographic processing, but this also may cause a clearance problembetween the bouncing reaction mass 110A and a linear motor, if used.Despite the downsides, one advantage of this configuration is that thegravity moments subtract from flexure moments, which reduces oreliminates the re-centering force.

Similarly, as shown in the depiction of linear spring 100B in FIG. 1B,when both flexures 115B are attached to the baseframe 100B at their topend and to reaction mass 110B at their bottom end, reaction mass 110Bfollows a smile-shaped arc 116B upon acceleration of a coupled stage(not shown). In other words, the flexures 115B each shorten with aquadratic error, and have similar effects as in the prior example.However, when this occurs, gravity moments plus the flexure moments addto produce a strong re-centering force. The stronger the re-centeringforce, the larger the load on the reaction masses, therefore requiringlarger motors.

Even though linear spring examples 100A and 100B, above, have theadvantages of being mechanically compact and able to be designed withvery low horizontal stiffness, the disadvantages described aboveoutweigh these advantages. In both examples, the curved motion caused bythe quadratic error results in undesirable vertical reaction forces.

As can be seen in the previously-described examples, an action oracceleration by a linear stage in a lithographic processing system maycause various undesirable reactions to those elements directly orindirectly connected to the stage, depending on the configuration used.These undesirable reactions include undesirable movements of thelithographic system, which may degrade or break various mechanicalportions of the system over time or may cause diminished quality inlithographic processing.

The present invention provides a simplified, more cost-effective way ofusing any type of bearings for supporting and guiding a reaction masslocated inside a controlled environment. In a controlled environment(e.g., a high vacuum or high purity gas environment), the inventionallows the use of bearings while preventing contamination of theenvironment by contaminants usually associated with bearings, such asgas used in gas bearings or lubricants used in roller bearings. It willbe appreciated, however, by those skilled in the art, that the presentinvention is easily adapted for use in atmospheric pressure as well.

A reaction mass mechanism according to the present invention isillustrated in FIG. 3. A reaction mass mechanism assembly 300, shown asa side view, includes a stage 320 coupled to at least one reaction mass310 via at least two stage bearings 325. Stage 320 can comprise, but isnot limited to, a reticle stage or a substrate stage, both used inlithography systems. In this example, stage 320 is a substrate stage,carrying substrate 370. Lithographic exposure means 372 is also shown.Lithographic exposure means 372 includes an illuminator with which toilluminate a mask located on a mask stage and a projection optics withwhich to project an image of the illuminated mask onto substrate 370located on substrate stage 320. Stage bearings 325 can be any type ofbearing (e.g., ball bearings, roller bearings, wheels, fluid bearings(including liquid or pressurized gas), etc.). However, if used in acontrolled environment, stage bearings 325 should be bearingsappropriate for this environment. In the embodiment shown, stage 320 isdriven via a conventional linear drive motor consisting of linear coil330 and magnet array 335, the magnet array 335 attached to reaction mass310.

In an embodiment involving a controlled environment 355, enclosure 350encloses stage 320 holding substrate 370, reaction mass 310, stagebearings 325, linear drive motor coil 330, and magnet array 335.Enclosure 350 can further enclose lithographic exposure means 372.Reaction mass 310 is supported by at least three baseframe bearings 360that are coupled to a baseframe 305. In an embodiment, baseframe 305 isuncoupled from enclosure 350, as shown in FIG. 3. In another embodiment,baseframe 305 is coupled to enclosure 350 by rigid supports (not shown).In yet another embodiment, baseframe 305 is coupled to enclosure 350 byflexible supports (not shown).

For achieving a leakproof seal between the bellows and the balance mass,it may be desirable to use a reaction mass 310 made out of a metalinstead of the more-common porous granite. For example, reaction mass310 can be made of stainless steel. Alternatively, metal plates 371 canbe coupled to a granite reaction mass, such that the bearings and thebellows interface with the metal plates instead of the granite. Forexample, bearings can slide along metal plates 371. Additionally, thebellows can be directly welded to the metal plates to produce aleakproof seal.

Baseframe bearings 360 can be any type of bearing (e.g., ball bearing,roller bearing, wheel, fluid bearing (including liquid or pressurizedgas), etc.). Each baseframe bearing 360 is separated from controlledenvironment 355 via a bellows 365. Bellows 365 can be made from verythin sheets of metal (such as stainless steel, for example), howeverother materials can be effectively used. To minimize stiffness in alldirections, bellows are generally constructed from as thin a material aspractical for their usage. In this type of application, bellows 365 areconstructed from material that is on the order of 0.025 cm(approximately 0.01 inch) thick. The inside diameter of bellows 365 mustbe at least large enough to contain a baseframe bearing 360 plus thelength of reaction mass 310 displacement. For bellows 365 of weldedconstruction, it is recommended that the outside diameter be about 5 cm(approximately 2 inches) larger than that of the inner diameter. Toachieve a low lateral stiffness, which is desirable to minimizetransmitting reaction forces to enclosure 350 through bellows 365, it isrecommended that the height of the bellows be about the same or greaterthan the outside diameter. The tops of the bellows 365 are coupled toreaction mass 310. The bottoms of the bellows 365 are coupled toenclosure 350. In an embodiment, the top of a bellows 365 is coupled toreaction mass 310 via top flange 475, as depicted in FIG. 4. Bellowsclose-up view 400 also depicts the bottom of bellows 365 coupled toenclosure 350 via bottom flange 480. Bellows 365 can be welded to flange475, or fastened by other conventional means.

Referring again to FIG. 3, bellows 365 are flexible enough to move withthe reaction mass, yet form a seal to prevent contaminants related tobaseframe bearings 360 from contaminating controlled environment 355. Inthis way, bellows 365 maintain a pressure separation between the volumeof bellows 365 and the volume of controlled environment 355. It will beappreciated that for some embodiments, it is not necessary for enclosure350 to enclose bellows 365 completely as is shown in FIG. 3.Alternatively, the volume of bellows 365 can be open to the atmosphere,while still maintaining a seal separating the volume of bellows 365 fromcontrolled environment 355.

Bellows 365 have only a limited range of motion. Therefore, bellows 365need to be large enough to accommodate the size of a baseframe bearing360 for the required amount of relative motion between the bearing andthe reaction mass. It will be appreciated by those skilled in the artthat bellows can also be used with stage bearings 325, thus enabling thestage itself to be supported by planar air bearings. However, stage 320has typically a much larger range of motion than its associated reactionmasses, which may be too large for ordinary metal bellows toaccommodate.

As described earlier herein, upon movement in one direction of a stagein a lithography system, the reaction mass(es) coupled to the stage willmove in the opposite direction to prevent the transfer of the reactionforce to the rest of the lithography system. The mass of the stage andthe reaction mass(es) determine how far the reaction mass will need tomove for this reaction force compensation. Applying the principle ofconservation of momentum to an example, if the total mass of thereaction mass is X times greater than the mass of the stage, then thereaction mass will move, in the opposite direction as the stage, a totalof 1/X the distance of the stage The coil portion of the linear motorsupplies a force equal to the stage mass times the acceleration of thestage. The magnet track portion of the linear motor experiences an equaland opposite force, which it transfers to the reaction mass,accelerating it at 1/X the rate of the stage. The vacuum chamberexperiences a horizontal force equal to the combined lateral stiffnessof the bellows times the displacement of the reaction mass. If thevacuum chamber is uncoupled from the baseframe, the baseframeexperiences no reaction force.

An additional advantage of this setup is that the center of gravity ofthe entire structure of the lithography system remains in place, thusthe baseframe experiences no tilting moments due to shifts in the centerof gravity of the components that it supports.

Referring to FIG. 3, for example, if stage 320 moves 300 mm(approximately 12 inches), and reaction mass 310 weighs 10 times greaterthan stage 320, then reaction mass 310 will move {fraction (1/10)} thedistance of stage 320 (i.e., reaction mass 310 will move 30 mm(approximately 1.2 inches)). In other words, the heavier the reactionmass, the shorter the distance the reaction mass will need to move inorder to perform reaction force compensation. It will be appreciatedthat a heavy reaction mass does not necessarily mean a large reactionmass. The present invention is most effectively used with a heavierreaction mass that only requires movement of a small distance. Forheavier reaction masses that only require traveling a short distance,short bearings can be used because the bellows will not need to flexvery far. Bellows allow only a limited range of motion and therefore aremore effective when used with reaction masses that only requiretraveling a short distance.

It will be appreciated that as few as three baseframe bearings can beused to support the reaction mass at three non-colinear points defininga plane. It will also be appreciated that there is no need for thebaseframe bearings to be along the entire length of the reaction mass.

A partial side view of a reaction mass bearing arrangement, according toan embodiment of the present invention, is depicted in FIG. 5. Aspartial side view 500 illustrates, an embodiment of the presentinvention includes reaction mass 310 shaped in such a way as to allowthe use of at least one additional bearing alongside stage 320 andreaction mass 310 in a plane perpendicular to the plane defined bybaseframe bearings 360. For example, baseframe side guidance bearings590 along with baseframe side guidance bellows 595 linearly guidereaction mass 310. Baseframe side guidance bearings 590 and baseframeside guidance bellows 595 are basically baseframe bearings 360 andbellows 365 repositioned to the side of reaction mass 310. Similarly,stage side guidance bearings 585 linearly guide stage 320. Stage sideguidance bearings 585 are basically stage bearings 325 repositioned tothe side of stage 320. These side support bearings 585, 590 horizontallyguide the movement of stage 320 and reaction mass 310 duringlithography.

CONCLUSION

Among the many discussed advantages of this invention, the embodimentsof this invention provide reaction mass bearing arrangements forlithography systems that are far simpler than compound flexurearrangements that have been proposed. Unlike simple flexure guides, thisinvention produces substantially straight or in-plane motion as opposedto arcuate motion, while keeping cost, size, and weight of the systemlow. The invention also provides very effective reaction mass bearingarrangements for lithography systems used in controlled environmentsthat are not restrained to using non-contaminant types of bearings.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details can be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A reaction mass apparatus comprising: a baseframe; at least onereaction mass, movably coupled to said baseframe by at least three firstbearings, and coupled to a stage by at least two second bearings and atleast one drive; and a plurality of bellows, each of said plurality ofbellows surrounding a corresponding one of said at least three firstbearings, wherein each of said plurality of bellows has a first endcoupled to said at least one reaction mass.
 2. The apparatus of claim 1,wherein each of said plurality of bellows has a second end coupled tosaid baseframe.
 3. The apparatus of claim 1, wherein said at least threefirst bearings are fluid bearings.
 4. The apparatus of claim 3, whereinsaid fluid is a pressurized gas.
 5. The apparatus of claim 3, whereinsaid fluid is a liquid film.
 6. The apparatus of claim 1, wherein saidat least three first bearings are roller bearings.
 7. The apparatus ofclaim 1, wherein said at least three first bearings are ball bearings.8. The apparatus of claim 1, wherein said at least one drive eachcomprises: a linear motor coil coupled to said stage; and a magnet arraycoupled to one of said at least one reaction mass, wherein said linearmotor coil and said magnet array are coupled magnetically.
 9. Theapparatus of claim 1, further comprising: an enclosure having acontrolled environment and enclosing said stage, said at least twosecond bearings, said at least one drive, and said at least one reactionmass, wherein each of said plurality of bellows separates saidcorresponding first bearing from said controlled environment.
 10. Theapparatus of claim 9, wherein each of said plurality of bellows has asecond end coupled to said enclosure.
 11. The apparatus of claim 9,wherein a volume enclosed by each of said plurality of bellows has apressure independent of the volume enclosed by said enclosure.
 12. Theapparatus of claim 9, wherein a flange couples said bellows first end toone of said at least one reaction mass.
 13. The apparatus of claim 12,wherein said flange comprises a sliding surface for an enclosed firstbearing.
 14. The apparatus of claim 9, wherein a flange couples saidbellows second end to said enclosure.
 15. The apparatus of claim 9,wherein said baseframe is uncoupled from said enclosure.
 16. Theapparatus of claim 9, wherein said baseframe is coupled to saidenclosure via rigid supports.
 17. The apparatus of claim 9, wherein saidbaseframe is coupled to said enclosure via flexible supports.
 18. Theapparatus of claim 9, wherein said enclosure further encloseslithographic exposure means.
 19. The apparatus of claim 1, wherein aflange couples said bellows first end to one of said at least onereaction mass.
 20. The apparatus of claim 1, wherein a flange couplessaid bellows second end to said baseframe.
 21. The apparatus of claim 1,wherein at least one of said first bearings is positioned such that itlinearly guides one of said at least one reaction mass.
 22. Theapparatus of claim 1, wherein the mass of said stage is X times lessthan the mass of said at least one reaction mass, resulting in said atleast one reaction mass moving, upon movement of said stage, a distance1/X the distance of said stage.
 23. The apparatus of claim 1, whereinsaid at least one reaction mass is made of metal.
 24. The apparatus ofclaim 1, wherein each of said plurality of bellows is made of metal. 25.A scanning apparatus used for lithographic processing within acontrolled environment, comprising: lithographic exposure means; abaseframe; at least one reaction mass movably coupled to said baseframeby at least three first bearings; a stage, coupled to said at least onereaction mass by at least two second bearings and at least one drive; anenclosure, having a controlled environment and enclosing saidlithographic exposure means, said stage, said at least two secondbearings, said at least one drive, and said at least one reaction mass;and a plurality of bellows, each of said plurality of bellowssurrounding a corresponding one of said at least three first bearingsand separating said corresponding first bearing from said controlledenvironment, wherein each of said plurality of bellows has a first endcoupled to said at least one reaction mass and a second end coupled tosaid enclosure.
 26. The scanning apparatus of claim 25, wherein said atleast three first bearings are fluid bearings.
 27. The scanningapparatus of claim 26, wherein said fluid is a pressurized gas.
 28. Thescanning apparatus of claim 26, wherein said fluid is a liquid film. 29.The scanning apparatus of claim 25, wherein said at least three firstbearings are roller bearings.
 30. The scanning apparatus of claim 25,wherein said at least three first bearings are ball bearings.
 31. Thescanning apparatus of claim 25, wherein said at least one drive eachcomprises: a linear motor coil coupled to said stage; and a magnet arraycoupled to one of said at least one reaction mass, wherein said linearmotor coil and said magnet array are coupled magnetically.
 32. Thescanning apparatus of claim 25, wherein a volume enclosed by each ofsaid plurality of bellows has a pressure independent of the volumeenclosed by said enclosure.
 33. The scanning apparatus of claim 25,wherein a flange couples said bellows first end to one of said at leastone reaction mass.
 34. The scanning apparatus of claim 25, wherein aflange couples said bellows second end to said enclosure.
 35. Thescanning apparatus of claim 25, wherein said baseframe is uncoupled fromsaid enclosure.
 36. The scanning apparatus of claim 25, wherein saidbaseframe is coupled to said enclosure via rigid supports.
 37. Thescanning apparatus of claim 25, wherein said baseframe is coupled tosaid enclosure via flexible supports.
 38. The scanning apparatus ofclaim 25, wherein at least one of said first bearings is positioned suchthat it linearly guides one of said at least one reaction mass.
 39. Thescanning apparatus of claim 25, wherein the mass of said stage is Xtimes less than the mass of said at least one reaction mass, resultingin said at least one reaction mass moving, upon movement of said stage,a distance 1/X the distance of said stage.
 40. The scanning apparatus ofclaim 25, wherein said at least one reaction mass is made of metal. 41.The scanning apparatus of claim 25, wherein each of said plurality ofbellows is made of metal.